This invention generally relates to improvements in light collection systems providing light beams for projectors and, more particularly, to a constant magnification light collection system of improved efficiency for use in light valve projectors.
Typical prior art color projection systems of the light valve type, as shown in U.S. Pat. No. 3,290,436 to W. E. Good et al. and U.S. Pat. No. 3,325,592 to W. E. Good et al., include a light collection system having an arc lamp located at the adjacent focus of a simple ellipsoidal reflector. A light beam is reflected from the ellipsoidal reflector through a pair of spaced lens plates having corresponding pluralities of rectangular lenticules stacked into horizontal rows and vertical columns. The second lens plate carries the input light mask of a schlieren optical system. With this arrangement, efficient utilization is made of light from the arc lamp, and uniform distribution of light is produced on the light modulating medium.
The basic light collection system disclosed in the Good et al. patents has been improved by the use of a compound reflector as disclosed in U.S. Pat. No. 4,305,099 to Thomas T. True et al. In the True et al. light collection system, the compound reflector is formed of full, uninterrupted surfaces of revolution in combination with spaced lens plates, each having a plurality of lenticules, to provide increased light collection efficiency while maintaining uniform light flux density. In the preferred embodiment of that invention, an ellipsoidal reflector is positioned behind the arc, and a spherical reflector is positioned forward of the arc and outside the outer acceptance limit of the beam. Other combinations are disclosed including positioning the forward spherical reflector within the inner acceptance limit of the beam and positioning the ellipsoidal reflector forward of the arc with the spherical reflector behind the arc.
The compound reflector system as described in the True et al. patent provides high light efficiency, but it has the disadvantages that it is expensive to produce and requires very precise alignment of the multiple-mirror components. What is needed is a light collection system for light valve projectors which exhibits similar high light efficiencies but is less complex to produce and align and potentially less expensive.